WLAN network information caching

ABSTRACT

A WLAN client device maintains a history of profile-location associations. An association links a profile stored in the client device with a location in the vicinity of which the client device was connected to a wireless local area network matching the profile. While in a vicinity of a certain location, the client device may scan for wireless local area networks in a manner that takes into account records of the history that include the certain location.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/876,455, filed Oct. 22, 2007, which is expected to issue on Aug. 14,2012 as U.S. Pat. No. 8,244,241, and which in turn claims priority under35 USC 119(e) from U.S. Provisional Patent Application No. 60/862,658,filed Oct. 24, 2006, the contents of which are incorporated by referenceherein.

BACKGROUND

A wireless local area network (WLAN) client device may store in itsmemory one or more profiles of wireless local area networks. A profilemay include, for example, the service set identity (SSID) of thenetwork, WLAN configuration parameters, security credentials, andInternet Protocol (IP) network parameters. The SSID is also known as thenetwork name. The profiles may be assigned priorities, for example, by auser that has purchased the client device, a carrier who controls thesale of the client device, or an administrator of an enterprise that haspurchased the client device.

Scanning is the process of identifying existing networks. Upon beingoperatively coupled to a radio of the client device, a WLAN controllerof the client device may automatically initiate passive scanning Inpassive scanning, the WLAN controller generally listens for beaconframes broadcast by access points (APs), one communication channel at atime. The communication channels, and the time spent passively scanningon a communication channel, are defined by the WLAN standard and/orregulatory requirements. Beacon frames of a WLAN are broadcast atregular intervals, for example, roughly each 100 ms. The SSIDs of theprofiles stored in the client device are compared to the SSIDs includedin beacon frames received by the client device on a particularcommunication channel. The order in which SSIDs of profiles are comparedto the SSIDs of the scan results may be determined by one or morefactors. For example, the SSIDs of the profiles may be compared in orderof decreasing priority for the profiles. In another example, the SSIDsof the scan results may be compared in order of decreasing receivedsignal strength. If the SSID field of a received beacon frame matchesthe SSID of a particular profile, the WLAN controller may initiate anauthentication process and, if the authentication process is successful,may initiate an association or re-association process with the AP thatsent the beacon frame.

If the comparison does not result in any matches, then the client devicemay present a list of identified networks (based on the SSID fields ofany received beacon frames) to the user of the client device, so thatthe user can select which, if any, of the networks to join.

In active scanning, the WLAN controller transmits an active proberequest including an SSID on a communication channel on which theregulatory requirements allow active probing. The WLAN controller mayreceive one or more probe responses. The probe responses may be receivedwithin 15 ms of the transmission of the active probe request. The activeprobe request may include a particular SSID, in which case proberesponses will be received from APs in the vicinity that are hosting aWLAN having the particular SSID. Alternatively, the active probe requestmay include a “wild card” for an SSID and probe responses may bereceived from more than one network. In the latter case, the SSIDs ofthe profiles stored in the client device are compared to the SSIDsincluded in the probe responses. The order in which SSIDs of profilesare compared to the SSIDs of the scan results may be determined by oneor more factors. For example, the SSIDs of the profiles may be comparedin order of decreasing priority for the profiles. In another example,the SSIDs of the scan results may be compared in order of decreasingreceived signal strength. If the SSID included in a probe responsematches the SSID of a particular profile, the WLAN controller mayinitiate an authentication process and, if the authentication process issuccessful, may initiate an association or re-association process withthe AP that sent the probe response. If no probe responses are received,the client device may transmit the active probe request on a differentcommunication channel, or may transmit an active probe request includinga different SSID, or may put its radio into a sleep state.

A WLAN may have a suppressed SSID, in which case beacon frames for thatWLAN will not include the suppressed SSID. Likewise, an AP having asuppressed SSID may ignore probe requests including a “wild card” SSID,or may respond with a probe response which lacks the SSID. If the clientdevice stores one or more profiles having suppressed SSIDs, the clientdevice may actively scan for those profiles using an active proberequest including the suppressed SSID. An AP having a suppressed SSIDwill respond to such an active probe request with a probe response whichincludes the suppressed SSID, if the SSID of the network handled by theAP matches that in the active probe request.

For battery-operated client devices, the process of network discoveryand association in a timely manner consumes significant battery life.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and not limitation in thefigures of the accompanying drawings, in which like reference numeralsindicate corresponding, analogous or similar elements, and in which:

FIG. 1 is an illustration of various exemplary communication devices andsystems;

FIG. 2 is a block diagram of an exemplary client device;

FIG. 3 is a flowchart of an exemplary method for pruning a history ofprofile-location associations; and

FIG. 4 is a flowchart of an exemplary scanning scheme.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of embodiments.However it will be understood by those of ordinary skill in the art thatthe embodiments may be practiced without these specific details. Inother instances, well-known methods, procedures, components and circuitshave not been described in detail so as not to obscure the embodiments.

One or more profiles of wireless local area networks may be stored in aWLAN client device. The client device may maintain a history ofprofile-location associations. An association links a profile stored inthe client device with a location in the vicinity of which the clientdevice was connected to a wireless local area network described in theprofile.

The association may also include an indication of the communicationchannel on which the client device connected to the wireless local areanetwork. The association may also include an indication of a time atwhich the client device was connected to the wireless local areanetwork.

For example, the history may includes records of one or more of thefollowing formats:

location ID-profile name

location ID-profile name-channel ID

location ID-profile name-timestamp

location ID-profile name-channel ID-timestamp

Any other suitable format that includes the information to be recordedis also contemplated.

The history may also be populated with profile-location associations,where the association links a profile stored in the client device with alocation in the vicinity of which a wireless local area networkdescribed in the profile is known to exist, even if the client devicehas not yet connected to that wireless local area network. Theassociation may also include an indication of the communication channelon which the wireless local area network is operating. Theseassociations, or information from which these associations may begenerated, may be sent to the client device via a wireless local areanetwork or via any other wireless network over which the client deviceis able to communicate or via any other means, such as, a wired oroptical connection between the client device and a computer. The sourceof these associations, or the information from which these associationsmay be generated, may be a database that stores data regarding accesspoints, WLANs supported by the access points, known locations of theaccess points, channels used by the access points to support the WLANs,and the like.

The same profile may be associated with more than one location ID. Forexample, hotspots located at several different locations yet from thesame carrier may all use the same SSID, hence a profile for thatcarrier's hotspots may be associated in the history with more than onelocation ID where the client device connected to the hotspots. Likewise,the same location ID may be associated with more than one profile in thehistory. This may occur, for example, if more than one WLAN is availableat the same location, profiles for at least two of the WLANs are storedin the client device, and the client device has previously connected tothe at least two WLANs.

While in the vicinity of a certain location, the client device may scanfor wireless local area networks in a manner that takes into accountrecords of the client device's history that include the certainlocation.

For example, if the client device performs active scanning on aprofile-by-profile basis, in which a probe request includes the SSID ofa profile stored in the client device, then the client device may sendprobe requests for those profiles associated in the history with thecertain location and may refrain from sending probe requests with theSSIDs of profiles that are not associated in the history with thecertain location. By refraining from sending certain probe requests,active scanning in this manner may involve less power consumption thanactive scanning in which probe requests for all profiles stored in theclient device are sent. However, if a wireless local area network in thevicinity of the certain location has an SSID that is not in a profileassociated in the history with the certain location, the wireless localarea network will not be detected by this manner of active scanning.

In another example, if the client device performs active scanning on aprofile-by-profile basis, in which a probe request includes the SSID ofa profile stored in the client device, then the client device may sendprobe requests for those profiles associated in the history with thecertain location prior to sending probe requests with the SSIDs ofprofiles that are not associated in the history with the certainlocation. Since the SSIDs of profiles associated in the history with thecertain location are sought prior to the SSIDs of profiles that are notassociated in the history with the certain location, networks may bedetected faster than if the SSIDs of the profiles were scanned in anorder that doesn't take into account which profiles describe wirelesslocal area networks that the client device previously connected to inthe vicinity of the certain location.

In yet another example, the client device may place all or a portion ofits WLAN communication interface (which includes its WLAN radio) into alower power state when not in the vicinity of a location included in theclient device's history, so that scanning is not performed by the clientdevice when not in the vicinity of a location included in the clientdevice's history, and may place its WLAN communication interface in ahigher power state sufficient for scanning when in the vicinity of alocation that is included in the client device's history. In thisexample, scanning is performed only when there is an expectation, basedon the history, that a WLAN matching one of the profiles in the clientdevice will be detected. This may reduce the power consumption of theclient device, since scanning is not performed in locations where thereis no expectation of detecting a WLAN matching one of the profilesstored in the client device. For example, if the client device stores afirst profile for a WLAN at the home of the user of the client deviceand stores a second profile for a WLAN at the workplace of the user ofthe client device, and each of these profiles is associated in thehistory with the corresponding location, then when the user travels withthe client device between home and the workplace, no scanning will bedone. As the user approaches or arrives at home or the workplace,scanning will be performed and the WLAN, if active, will be detected.

In a further example, where the association includes an indication ofthe communication channel on which the client device connected to thewireless local area network, the client device may scan for wirelesslocal area networks on channels associated in the history with thecertain location and may refrain from scanning for wireless local areanetworks on channels that are not associated in the history with thecertain location. This may apply to passive scanning, active scanning orany combination thereof. By refraining from scanning on certainchannels, this manner of scanning may involve less power consumptionthan scanning on all channels. However, if a wireless local area networkin the vicinity of the certain location is on a channel that is not in aprofile associated in the history with the certain location, thewireless local area network will not be detected by this manner ofscanning The effect of this manner of scanning may be greater innetworks having many channels, such as IEEE 802.11a, than in networkshaving fewer channels, such as IEEE 802.11b or IEEE 802.11g.

In another example, where the association includes an indication of thecommunication channel on which the client device connected to thewireless local area network, the client device may scan for wirelesslocal area networks on channels associated in the history with thecertain location prior to scanning for wireless local area networks onchannels that are not associated in the history with the certainlocation. This may apply to passive scanning, active scanning or anycombination thereof. Since the channels associated in the history withthe certain location are scanned prior to the channels that are notassociated in the history with the certain location, networks may bedetected faster than if the channels were scanned in an order thatdoesn't take into account on which channels the client device previouslyconnected to wireless local area networks when in the vicinity of thecertain location.

The client device may employ any combination of the modificationsdescribed hereinabove.

The client device may determine its current location using any suitablemethod. The current location as determined by the client device need notbe precise. It may be sufficient that the location thus determined bedistinguishable from other locations identified in the history.

For example, the client device may be equipped with or coupled to aglobal positioning system (GPS) receiver and able to obtain its GPScoordinates from received signals that originate from a system of GPSsatellites. The location ID in the history may be related to the GPScoordinates. Using information that is included in signals received viathe GPS receiver, the GPS receiver or a processor of the client deviceor both may be able to estimate the geographic location of the clientdevice. The accuracy of location estimation using GPS is subject toerrors due to Ionospheric effects, Ephemeris errors, Satellite clockerrors, Multipath distortion, Tropospheric effects, Numerical errors andother errors, and may be in the range of approximately 2 meters to 20meters.

In another example, the client device may be able to communicate with abase station of a cellular network system and to determine its locationfrom those communications. A non-exhaustive list of methods forestimating the location of a cellular device from signals received via acellular network interface includes RSS (received signal strength)positioning, E-OTD (Enhanced Observed Time Difference), TOA (time ofarrival) positioning, U-TDOA (Uplink Time Difference of Arrival), WLS(Wireless Location Signature), A-GPS (assisted GPS), ALFT, ELFT, RadioFingerprinting, AOA (Angle of Arrival) positioning, MNLS, CGI (CellGlobal Identity), CGI+Timing Advance, Enhanced Cell ID, and any otherappropriate method. With U-TDOA, for example, latitude and longitude canbe typically calculated with an accuracy of about 50 meters. A simplerversion may be for the client device to use the location of the cellularbase station as the location ID in the history. Alternatively, theclient device may use the cell id gleaned from signals received from thecellular base station as an indication of its current location. Similartechniques may be applied in the case where the client device has awireless network interface that is compatible with one or more wide areanetwork communication standards, such as IEEE 802.16, WiMAX andBroadband Wireless Access (BWA).

FIG. 1 illustrates various exemplary communication devices and systems.An AP 102 may belong to a first WLAN and an AP 103 may belong to asecond WLAN. WLAN client devices, for example, a handheld device 104 anda laptop computer 106, may search for and attempt to connect to wirelesslocal area networks.

Profiles of wireless local area networks may be stored in the WLANclient devices. For example, laptop computer 106 may store profiles of awork WLAN, a home WLAN, a hotspot and a hotel WLAN. In another example,handheld device 104 may store profiles of a work WLAN, a home WLAN andtwo hotspots that its user frequents.

Handheld device 104 or laptop computer 106 or both may be coupled to orequipped with a GPS receiver and may be able to determine theirlocations from signals received from GPS satellites, of which a singlesatellite 108 is shown.

Handheld device 104 or laptop computer 106 or both may have a wirelessnetwork interface and may be able to determine its location from signalsreceived from a base station 110.

FIG. 2 is a block diagram of an exemplary client device. A client device200 comprises a processor 202, and a memory 204 coupled to processor202. A cache 208 may also be coupled to or embedded in processor 202. Ahistory 209 of associations 211 may be stored in cache 208 for rapidaccess or may be stored in memory 204.

Client device 200 comprises a WLAN interface 210, compatible with one ormore WLAN standards, for example, one or more standards of the family ofIEEE 802.11 wireless communication standards. WLAN interface 210 iscoupled to processor 202 and includes at least a WLAN controller 212 anda radio 214. Client device 200 also comprises an antenna 216 coupled toradio 214. For example, client device 200 may be able to communicatewith APs via WLAN interface 210 and antenna 216.

Memory 204 stores code 206 that, when executed by processor 202, mayimplement the methods described herein together with WLAN controller212. Memory 204 also stores profiles 207 of wireless local areanetworks.

Client device 200 may also comprise a wireless communication interface220. Wireless communication interface 220 may be a wireless cellularnetwork communication interface. Wireless communication interface 220 iscoupled to processor 202 and includes at least a baseband controller 222and a radio 224. Radio 224 may be coupled to antenna 216, or clientdevice 200 may comprise an additional antenna 226 coupled to radio 224.Client device 200 may be able to communicate with base stations of acellular network via wireless communication interface 220 and antenna216 or 226. Alternatively, wireless communication interface 220 may be awide area network communication interface.

Client device 200 may also comprise a GPS receiver 230 coupled toprocessor 202, and an antenna 236 coupled to GPS receiver. GPS receiver230 may be considered a wireless interface.

Client device 200 includes other components that, for clarity, are notshown in FIG. 2. A non-exhaustive list of examples for client device 200includes a wireless-enabled laptop computer, a wireless-enabled tabletcomputer, a wireless-enabled cellphone, a wireless-enabled personaldigital assistant (PDA), a wireless-enabled smart phone, awireless-enabled video camera/monitor, a wireless-enabledgaming/multimedia console, a wireless-enabled sensor/reporting/storagedevice, a wireless Internet Protocol (IP) phone and any other suitableWLAN client device.

FIG. 3 is a flowchart of an exemplary method for pruning the history ofaged associations. At 302, the client device identifies which, if any,profile-location associations in the history have a timestamp thatindicates that the association is older than a time T. The time T may beconfigurable by the client device. If there are any associations olderthan T, as checked at 304, then at 306, those associations may bedeleted. After waiting a certain period of time, as indicated at 308,the method may resume from 302.

FIG. 4 is a flowchart of an exemplary scanning scheme to be implementedin a client device, for example, handheld device 104 or laptop 106.

At 402, the client device determines its current location. Variousmethods for the client device to determine its current location havebeen described hereinabove.

At 404, the client device checks whether the history has records thatinclude the current location.

If not, then at 406, the client device scans for WLANs as usual andcompares the scan results to the one or more profiles stored in theclient device. The scanning may be passive or active or involve acombination of the two types. Any suitable scanning algorithm may beused at 406. Any suitable method for comparing the scan results and theprofiles may be used at 406.

If there is a match, and the client device connects to a WLAN matchingone of the profiles, as checked at 410, then an association of theparticular profile and the current location may be included in thehistory at 412. The association may also include a timestamp. Theassociation may also include an indication of the communication channelon which the client device connected to the WLAN. If there are nomatches or an attempted connection does not succeed, the client devicemay present the scan results to the user at 414.

Returning to 404, if the history has records that include the currentlocation, then at 416, the client device scans for WLANs in a mannerthat takes into account records of the history that include the currentlocation, and compares the scan results to the one or more profilesstored in the client device. Examples of how the scan may take intoaccount records of the history have been described hereinabove. Anysuitable method for comparing the scan results and the profiles may beused at 416.

If there is a match, and the client device connects to a WLAN matchingone of the profiles associated in the history with the current location,as checked at 420, then the timestamp, if any, of the correspondingprofile-location association in the history may be updated at 422.Otherwise, the method may proceed to 410 where the client device checkswhether client device has connected to a WLAN matching a profile that isnot associated in the history with the current location.

Although the subject matter has been described in language specific tostructural features or methodological acts or both, it is to beunderstood that the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. A method in a wireless local area network clientdevice, the method comprising: maintaining a history of profile-locationassociations, where an association links a profile stored in the clientdevice with a location in a vicinity of which the client device wasconnected to a wireless local area network described in the profile andwhere the association includes an indication of a time at which theclient device was connected to the wireless local area network when inthe vicinity of the location; determining a current location of theclient device; comparing the current location of the client device tothe locations in the history; and responsive to determining that thereis no location in the history that corresponds to the current locationof the client device, scanning for wireless local area networks, whilein a vicinity of the current location, using a scanning algorithm thatis independent of any location in the history.
 2. The method of claim 1,further comprising: responsive to connecting to a wireless local areanetwork matching a profile that is not associated in the history withthe current location, including in the history an association of theprofile with the current location.
 3. The method of claim 2, furthercomprising: including in the association an indication of acommunication channel on which the client device connected to thewireless local area network.
 4. The method of claim 1, furthercomprising: updating the time indicated in the association responsive tothe client device subsequently connecting to the wireless local areanetwork when in the vicinity of the location.
 5. The method of claim 1,further comprising: responsive to being unable to connect to anywireless local area network, presenting results of the scanning to auser of the client device.
 6. The method of claim 1, wherein maintainingthe history further comprises: removing from the history associationsthat are older than a certain age.
 7. The method of claim 6, furthercomprising: configuring the certain age.
 8. A wireless client devicecomprising: a processor; a wireless local area network interface coupledto the processor, the wireless local area network interface comprising awireless local area network controller and a radio; an antenna coupledto the radio; another wireless interface coupled to the processor,through which the client device is able to determine its currentlocation; and a memory coupled to the processor, the memory arranged tostore profiles of wireless local area networks and arranged to storeexecutable code that, when executed by the processor, maintains ahistory of profile-location associations, where an association links aprofile stored in the client device with a location in a vicinity ofwhich the client device was connected to a wireless local area networkdescribed in the profile and where the association includes anindication of a time at which the client device was connected to thewireless local area network when in the vicinity of the location, causesthe wireless client device to compare the current location to thelocations in the history, and, responsive to determining that there isno location in the history that corresponds to the current location ofthe client device, controls the wireless local area network controllerto scan for wireless local area networks, while in a vicinity of thecurrent location, using a scanning algorithm that is independent of anylocation in the history.
 9. The wireless client device of claim 8,wherein the executable code, when executed by the processor, causes thewireless client device, responsive to connecting to a wireless localarea network matching a profile that is not associated in the historywith the current location, to include in the history an association ofthe profile with the current location.
 10. The wireless client device ofclaim 9, wherein the executable code, when executed by the processor,causes the wireless client device to include in the association anindication of a communication channel on which the client deviceconnected to the wireless local area network.
 11. The wireless clientdevice of claim 8, wherein the executable code, when executed by theprocessor, updates the time indicated in the association responsive tothe client device subsequently connecting to the wireless local areanetwork when in the vicinity of the location.
 12. The wireless clientdevice of claim 8, wherein the executable code, when executed by theprocessor, causes the wireless client device, responsive to being unableto connect to any wireless local area network, to present results of thescanning to a user of the client device.
 13. The wireless client deviceof claim 8, wherein the memory is arranged to store the history ofassociations.
 14. The wireless client device of claim 8, furthercomprising: a cache coupled to the processor, the cache arranged tostore the history of associations.
 15. The wireless client device ofclaim 8, wherein the other wireless interface comprises a globalpositioning system (GPS) receiver.
 16. The wireless client device ofclaim 8, wherein the other wireless interface comprises a wirelesscellular network communication interface.
 17. The wireless client deviceof claim 8, wherein the other wireless interface comprises a wirelesswide area network communication interface.
 18. The wireless clientdevice of claim 8, wherein the executable code, when executed by theprocessor, removes from the history associations that are older than acertain age.
 19. The wireless client device of claim 18, wherein thecertain age is configurable.